The behavioural ecology of the mara, Dolichotis patagonus
This thesis presents the results of a 3 year field study on the behavioural ecology of the mara on the Valdés Peninsula in Argentina. The main goal was to investigate why the mara's social system incorporates both monogamy and communal denning, a combination unknown in other mammals. The research techniques used were behavioural observations and radio-tracking. Radio-tracking of 9 maras revealed that pairs were continually moving into new areas, suggesting that their ranging behaviour is adapted to an irregular pattern of resource distribution. Two maras had prevailing ranges of 35 ha and moved yearly over about 200 ha. Ranges floated around a geographic centre. One constraint on the animals' movements may be the need to stay near a den site for pupping. Maras were diurnal, and spent on average 46% of the day grazing. Ranges may overlap up to 33%, but range use between neighbouring pairs were negatively correlated suggesting that animals were avoiding each other--pairs may be occupying floating territories. Evidence that maras are monogamous in the wild is presented. The factors leading to monogamy are argued to be: (i) females are irregularly dispersed because of the distribution of food; and (ii) the brevity of the female's oestrus (1-2 hrs). A male attempting to mate polygynously would have difficulties in finding and securing a female; thus males may do best by staying with one female to ensure a successful mating. Males may enhance their reproductive success by watching for predators so that their females can spend more time feeding to meet the energetic demands of lactation and gestation. During the pupping season, August to January, groups of 1 to 22 pairs gather at single dens. Several dens may be located near each other to form denning communities. Most pairs produce only one litter a year and there is a peak of births in September and October. Pairs visit the den once a day for a period of 5-6 weeks to nurse their young. Den sites are not limited; and the reason maras den communally appears to be the increased protection from predators accruing to pups and adults in larger groups. Two possible routes are suggested in the evolution of the mara's social system: (i) from a monogamous starting point it has become advantageous to creche pups; or (ii) ancestral maras were more colonial and probably polygynous, but have been forced to space out because of changes in the distribution of food, which has led to monogamy. Finally, maras were compared with other caviomorph rodents, lagomorphs, and monogamous ruminants and were shown to be most similar to the latter in their adaptations to the environment a remarkable example of convergent evolution.